I assume that uou are using a good quality beerkit, with a reasonable yeast?
eg Morgans, Muntons, Beermakers, ESB, Thomas Coopers (NOT Coopers std/Int'l), Brewcraft, or Blackrock.
Otherwise, did you add an updatesd yeast such as Safale or Saflager.
There is a wineyeast known as EC1118 (Premier...